This invention relates generally to fluid couplings and more particularly to sealing arrangements for fluid couplings.
Certain aircraft gas turbine engines employ fluid systems operating at higher than average pressures, and are thus prone to leakage. For example, in some applications, fuel at 28 MPa (4000 psi) is used as a working fluid to operate multiple engine actuators. Because of the high pressures and high fuel flows, a type of coupling known as a 4-bolt flange face seal is used to make fluid connections between the various components. Based upon extrusion analysis, a standard type of seal would require a thicker flange than what is normally used in moderate-pressure systems, in order to prevent the flange from lifting off the seal. This thicker flange adds weight to the overall design and the seal will still be susceptible to failure if the flange is not clamped properly during assembly.
Historically, 4-bolt flange face seals would incorporate one of two types of seal designs: (1) a combination metal and elastomer flange gasket, such as those sold under the GASK-O-SEAL brand name by Parker Hannifin Company, Cleveland, Ohio 44124 USA; or (2) a loose L-shaped cross-section elastomer seal with a mating backup ring. The standard flange gasket consists of a metal retainer plate with an elastomer seal on each side. The seal is permanently attached to the retainer plate for simplification in maintainability and assembly. One side of the seal is compressed against the flange and the other seal is compressed against the mating component or flange. The negative aspect of the flange gasket type design is that it is limited under high pressures and requires a small clearance gap to be maintained to prevent seal extrusion. This requires a thick, stiff flange connection to limit bending in the flange.
The loose L-shaped elastomer sits in a seal gland in the mating component or flange. A flange is then clamped over the seal to provide a compression force on the seal. This design has maintainability limitations, as there is no visual indicator that verifies that the seal is installed in the seal gland. The seal can also be installed in an inverted position that will cause the backup ring to be in the bottom of the gland, rendering it useless during operation. This type of seal also requires precision-machined glands in the flange for proper operation.